Leaf spring design for centrifugal clutch

ABSTRACT

A spring apparatus can be implemented, which includes a leaf spring for use in a clutch mechanism, wherein the leaf spring is configured to avoid coil clash and end wire lengths of the leaf spring are positioned in order to center the leaf spring without additional features thereof. Bend radii and a wire diameter associated with the leaf spring. The leaf spring can be adapted for use in a centrifugal clutch and/or automobile latch.

REFERENCE TO RELATED APPLICATION

This patent application claims priority under 35 U.S.C. § 119(e) toprovisional patent application Ser. No. 60/590,708 entitled “Latch andClutch Component Optimization Methods and Systems,” which was filed onJul. 23, 2004, the disclosure of which is incorporated herein byreference.

TECHNICAL FIELD

Embodiments are generally related to mechanical and electro-mechanicalactuators, such as clutch mechanisms. Embodiments are also related tolatch mechanisms and clutch mechanisms. Embodiments are additionallyrelated to centrifugal clutches and components thereof, such as, forexample, clutch springs. Embodiments are also related to automotivesystems, such as automobile door latch systems and transmission systems.

BACKGROUND OF THE INVENTION

Mechanical and electro-mechanical actuators are utilized in a variety ofapplications for operating devices and systems such automotive doorlatches, transmission systems, and so forth. An example of such amechanical or electromechanical actuator is a centrifugal clutch, suchas those used in power door lock operations.

In power door lock operations, for example, a drive motor can beutilized to reciprocally drive or shift a lift arm that is connected toa locking lever of a door latch assembly mounted in an automobile door.The lift arm is typically coupled to an output shaft of the drive motorvia an intermediate gear train and operates to position the lockinglever in either a locked or an unlocked position.

Additionally, the lift arm can be manually driven or shifted by eitherrepositioning a door lock knob or slider, or by use of a door key. Sincethe gear train and output shaft are directly coupled to the lift arm,manually shifting the lift arm into the locked position requires drivingthe gear train and the output shaft, and shifting the lift arm into theunlocked position requires back driving the gear train and the outputshaft. In both cases, the drive motor and gear train undesirably offerresistance to being manually driven/back driven by the door key, or byrepositioning the door lock slider. Relatively speaking, the drive motoroffers substantially greater resistance to being manually driven/backdriven than the gear train.

The ease with which a lift arm can be manually shifted by use of a doorkey or door lock slider is referred to as the key effort orreversibility of the power door lock system which is a measure of theamount of resistance provided by the drive motor and gear train when thelift arm is manually shifted. Thus, the greater resistance provided bythe gear train and the drive motor, the greater the key effort requiredto shift the lift arm and the higher the reversibility of the power doorlock system.

One solution to the problem of driving/back driving the motor duringmanual operation is by use of a clutch such as a centrifugal clutchinterposed between the output shaft of the drive motor and the geartrain. The clutch operates to selectively mechanically couple the outputshaft of the motor to the lift arm when the motor is activated, such asduring a power door lock or unlock operation, and to decouple the outputshaft from the lift arm when the motor is deactivated to thereby permitmanual shifting of the lift arm without additionally driving/backdriving the motor.

Thus, when the clutch decouples the motor from the lift arm, the keyeffort required to unlock the car door with a key, or by repositioningthe door lock slider is desirably reduced. The key effort is reducedbecause only the lift arm, jack screw and gear train are driven/backdriven without additionally driving/back driving the motor.

Centrifugal clutches for use in selectively establishing a mechanicaldriving connection between the output shaft and the lift arm have beenimplemented. A centrifugal clutch can be interposed between a drivemotor output shaft and a gear train of a power door lock actuator. Anexample of such a conventional centrifugal clutch is disclosed in U.S.Pat. No. 5,862,903, “Centrifugal Clutch for Power Door Locks”, whichissued on Jan. 26, 1999 and is incorporated herein by reference. One ofthe problems with conventional centrifugal clutch mechanisms is thatsuch a device includes numerous parts such as springs, which cancomplicate the clutch design, reduce operational reliability of theclutch, complicate the manufacturing and assembly process, andultimately increase manufacturing and maintenance costs, particularly ifdevices such as the springs are inherently flawed due to poor designconfigurations, which are inherently subject to stress and breakage, andultimately poor life spans.

Background for the First Embodiment

Some latch designs contain a spring with an axis parallel to the planeof intermediate sliders with two legs contacting each side of point C sothat movement in either direction constitutes coiling of the spring.Such a design is inadequate because the movement of the spring is notpurely in coiling the spring, but also along the axis, which functionsto spread or compress the coils together. The stress on the two legs isthus too great, leading to premature failure of the latch incorporatingsuch a spring and intermediate sliders.

Background for the Second Embodiment

Automatic latching systems may require the use of a clutch springmechanism that includes a return spring, which generally biases thelocation of the abutment to the disengaged position. Some conventionaldesigns can be overstressed, which leads to a short life cycle for theclutch spring mechanism. For example, the clutch and/or clutch springmechanism can fracture during clutch testing.

It is thus desirable to optimize latching system components, such as,for example, spring mechanisms and in particular, clutch springmechanisms and devices. The principal requirements for a successfulspring design including tightening manufacturing tolerances, determiningwhich forces the design actually requires (e.g., low and upper limits),and determining the maximum allowable footprint for the channel in orderto provide the maximum design space available for further optimizationand for meeting such requirements.

FIG. 1 illustrates a stress plot 100 for a conventional latch spring,which can be evaluated in order to determine optimal parameters for thedesign of an improved latch spring. Such a latch spring can be formedfrom a material such as, for example, BS-2056 302S26 (e.g., springtemper 302 SST), which is a very strong material having a tensilestrength of approximately 325 kpsi. A Table A is illustrated below inassociation with FIG. 1 in order to summarize design iteration resultsfor such an automotive latch spring. In Table A, all dimensions are inmm, all forces are in pounds, and stresses are in kpsi. Stress plot 100of FIG. 1 is therefore associated with Table A.

FIG. 2 illustrates a stress plot 200 for a conventional latch spring,which can be evaluated in order to determine optimal parameters for thedesign of an improved latch spring. Again, such a latch spring can beformed from a material such as, for example, BS-2056 302S26 (e.g.,spring temper 302 SST), which is a very strong material having a tensilestrength of approximately 325 kpsi. A Table B is shown below inassociation with FIG. 2, in order to summarize design iteration resultsfor such an automotive latch spring. In Table B, all dimensions are inmm, all forces are in pounds, and stresses are in kpsi. Stress plot 200is therefore associated with Table B. TABLE B Wire Outer Force ForceCase Dia. Length Width Loop R #Loops Assmb'd Compr'd Stress ConstantLength 0.25 12.50 7.80 0.333 4.5 0.049 0.098 173.9 0.30 12.50 7.80 0.404.5 0.101 0.207 199.1 0.35 12.50 7.80 0.467 4.5 0.185 1.517* 328.5* 0.4012.50 7.80 0.533 4.5 0.314* 34.782* 1120.0* Variable Length 0.25 10.667.80 0.333 4.5 0.013 0.062 109.9 0.30 12.50 7.80 0.40 4.5 0.101 0.207199.1 0.35 14.34 7.80 0.467 4.5 0.321 1.588* 388.7* 0.40 16.18 7.800.533 4.5 0.773 30.317* 1130.0*

Note that FIGS. 1 and 2 along with Tables A-E described herein arereferenced in order to explain why conventional latch springs do notmeet the aforementioned principal requirements for a successful springdesign, including tightening manufacturing tolerances, determining whichforces the design actually requires (e.g., low and upper limits), anddetermining the maximum allowable footprint for the channel in order toprovide the maximum design space available for further optimization andfor meeting such requirements.

In general, the spring wire diameter can be adjusted in steps of 0.05 todetermine the effect on performance. At the same time, a constant levelof forming strain can be maintained at the corner bend radius. This isthe strain that a manufacturer may require to incorporate into thematerial during the forming process, and is equivalent to the wirediameter divided by the diameter of the bend at the wire center line.This situation can be seen by looking at Table B and noting how the loopouter radius increases as the wire diameter also increases. Such aseries can be repeated twice, first keeping the length constant and thenallowing the length to increase or decrease based on corner bend radiuschanges, while maintaining all other aspects of the spring designconstant.

One interesting phenomenon can occur when all of the loops begin tocontact each other when the spring is at a full compression thereof. Theforces and stresses increase. The reason for such an occurrence is thatessentially all of the extra space is taken up, the loops collapse, andessentially only the loop ends begin to compress. FIG. 2 essentiallydemonstrates the stress plot 200 for the collapsed spring. The arrows204 drawn between the loops shown reaction forces between loops that arein contact. Note that only a line is drawn rather than the full wirediameter (i.e., because line elements are utilized), but that loops donot become closer to each other or to the channel side walls than onewire diameter, because the wire thickness is taken into account in sucha model.

The data of Tables A and B and stress plots 100 and 200 lead to aconclusion that wire diameter possesses a strong relationship tocompression forces and stresses. In such tables and stress plots, adirect effect is due to wire diameter. Such an effect, however, is alsoan indirect result of the loop corner radius because it is increased tomaintain the same wire corner radius/diameter ratio. Additionally, suchan effect is also an indirect result of the spring length, which changeswith wire diameter and outer loop radius. The effect on compressionforce is generally exaggerated for the last two cases (i.e., seeconstant length and variable length of Table B) because full loopcompression occurs. Even disregarding this, however, it is interestingto note that the effect remains strong. Obviously, the smallest wirediameter can meet operating force requirements is best from a stresspoint of view.

Three independent optimizations can be run with the number of loops setat 3.5, 4.5, and 5.5, as indicated at Table C in order to determine ifany designs better than prior designs can be found. The criteriautilized in such a scenario is that the spring should meet all forcerequirements (e.g., 0.100±0.008 lbs in the assembled position and0.200±0.016 lbs in the compressed position), while not contacting theside rails during actuation. A further requirement is that all cornerbend radii should possess low forming strain (e.g., bending radius towire diameter ratio, in this case, equivalent to a 0.3 mm diameter benton a 0.4 wire mm radius), so they would be manufacturable. Thus, theoptimum design is preferably the one that possesses the lowest stress ina fully compressed state, which correlates directly to the longest life.TABLE C Wire Outer Force Force Case Dia. Length Width Loop R #LoopsAssmb'd Compr'd Stress 0.231 13.444 6.359 0.670 3.5 0.107 0.184 345.30.300* 12.500* 7.800* 0.700* 4.5* 0.099* 0.205* 197.7* 0.251 13.4546.395 0.618 5.5 0.102 0.191 243.6

In evaluating the data in Table C, it is important to note that droppingthe number of loops to 3.5 results in an optimum that develops nearlytwice the stress of 4.5 turns, and is represents the wrong direction forproceeding in latch spring design development. Increasing the number ofloops to 5.5 offers more promise. Although the stress values in Table Cdemonstrate that 4.5 turns is better, 5.5 turns remains a preferredvalue. Intuitively, adding more turns means adding more wire, whichlowers the stress. The only manner, in which more wire can be added,however, is if the maximum allow able length increases. The 5.5 turns iscramped, and tight corner radii are required to fit thereof, whichproduces higher corner stress. If another millimeter is allowed, such aparameter would permit the bend radius to increase slightly, which wouldlower stresses possibly below the 4.5 loop case stress. Increased lengthwould obviously help the 4.5 loop case of Table C.

The question of whether stress levels are low enough to produce adequatelife of a latch spring configuration depends on several factors. Atypical rule of thumb is that stresses should be 50% of the ultimatetensile strength for infinite life. In this case, that would be 162.5ksi, but the best optimal design remains above this value. Additionally,there is some mean stress always present due to the pre-load in thespring, and this will lower the fatigue life even more. Infinite life,however, may not be what is required. The only dependable answer is torely on test data to determine if the design is adequate.

Tables D and E respectively represent additional data with respect to aconventional 4.5 loop configuration and a conventional 5.5 loopconfiguration. To interpret both tables, note that “r” indicates theouter loop radius and the value thereafter refers to length, while “w”refers to width, and “d” to wire diameter. “All” indicates that all ofthese variables are changed simultaneously. TABLE D Wire Outer ForceForce Case Dia. Length Width Loop R #Loops Assmb'd Compr'd Stress Nom.:0.30 12.46 7.64 0.70 4.5 0.106 0.218 205.8 r − .1 0.30 12.46 7.64 0.604.5 0.109 0.220 218.3 r + .2 0.30 12.46 7.64 0.90 4.5 0.099 11.269*857.0* w − .26 0.30 12.46 7.38 0.70 4.5 0.117 0.240 220.0 w + .26 0.3012.46 7.90 0.70 4.5 0.096 0.198 192.9 l − 1.5 0.30 10.96 7.64 0.70 4.50.041 0.149 147.4 l + 1.5 0.30 13.96 7.64 0.70 4.5 0.169 0.288 271.1 d −.02 0.28 12.46 7.64 0.68 4.5 0.080 0.161 196.2 d + .02 0.32 12.46 7.640.72 4.5 0.137 0.291 222.3 all (−) 0.28 10.96 7.38 0.58 4.5 0.036 0.129151.7 all (+) 0.32 13.96 7.90 0.92 4.5 0.189 15.487* 976.3

TABLE E Wire Outer Force Force Case Dia. Length Width Loop R #LoopsAssmb'd Compr'd Stress Nom.: 0.252 13.454 6.395 0.618 5.5 0.103 0.193244.1 r − .1 0.252 13.454 6.395 0.518 5.5 0.107 0.184 254.2 r + .2 0.25213.454 6.395 0.818 5.5 0.098 13.606* 1360.0* w − .26 0.252 13.454 6.1350.618 5.5 0.116 0.217 262.6 w + .26 0.252 13.454 6.655 0.618 5.5 0.0920.172 227.6 l − 1.5 0.252 11.954 6.395 0.618 5.5 0.058 0.141 178.7 l +1.5 0.252 14.954 6.395 0.618 5.5 0.147 0.247 307.9 d − .02 0.232 13.4546.395 0.598 5.5 0.073 0.131 221.0 d + .02 0.272 13.454 6.395 0.638 5.50.140 0.291 265.9 all (−) 0.232 11.954 6.135 0.498 5.5 0.049 0.111 189.6all (+) 0.272 14.954 6.655 0.838 5.5 crashed, no data (but very high)

The aforementioned Tables A-E and associated stress plots indicate thattolerances are very loose as compared to what is required. If aconventional spring latch is utilized as the maximum allowable assemblyand compressed forces, then the conventional spring mechanism designsassociated with Tables A-E and associated stress plots exceed theselevels when tolerances are at their extremes.

The data associated with Tables A-E and the associated stress plots,indicates that the conventional spring upon which such data is based isbarely able to meet the aforementioned principal requirements for asuccessful spring design, thereby rendering any designs based on such aconventional spring as unsatisfactory. Chief areas of concern for such aconventional spring design are that the stresses are too high, which canlead to poor fatigue life and also, that the manufacturing tolerancesare too large to meet performance requirements.

Background for the Third Embodiment

A conventional clutch mechanism contains a return spring, which biasesthe location of the abutment to the disengaged position. Such a springis typically implemented as a flat spring with multiple bends thatprovide the return force for the clutch slider when compressed. Suchconventional clutch mechanisms and spring designs typically becomeoverstressed, which leads to a short cycle life. Such conventionalconfigurations may fracture during clutch testing after less than, forexample, 26,000 cycles. Such a conventional design also incorporates abend at each end of the wire, which can cause coil clashing uponcompression.

Background for the Fourth Embodiment

Conventional centrifugal clutches typically suffer from imbalance duringoperation, particularly in the context of motor and clutch assemblies.Such assemblies typically remain unbalanced during performanceconditions. For example, upon testing a conventional clutch on a motorfor 26,000 cycles, it has been observed that motor bearings wearsignificantly and therefore are predicted not to withstand the requiredcycles. Such an assembly must be accurately balanced in order to improvevibration and bearing life in the motor. Despite efforts to implementbalancing in a centrifugal clutch such as, for example, utilizingsoftware analysis tools to properly balance the centrifugal clutchassembly, it has been determined that such designs when subject totesting can wear away the contacts in the motor.

BRIEF SUMMARY OF THE INVENTION

The following summary of the invention is provided to facilitate anunderstanding of some of the innovative features unique to the presentinvention and is not intended to be a full description. A fullappreciation of the various aspects of the invention can be gained bytaking the entire specification, claims, drawings, and abstract as awhole.

It is, therefore, one aspect of the present invention to provide forlatch and clutch optimization methods and systems.

It is another aspect of the present invention to provide for methods andsystems for optimizing intermediate sliders utilized in association witha spring in latch mechanisms.

It is a further aspect of the present invention to provide for methodsand systems for optimizing clutch spring mechanisms.

It is yet an additional aspect of the present invention to provide for aleaf spring mechanism for use in a centrifugal clutch assembly.

It is also an aspect of the present invention to provide for methods andsystems for balancing a centrifugal clutch.

The aforementioned aspects of the invention and other objectives andadvantages can now be achieved as described herein. Latch and clutchcomponent optimization methods and systems are disclosed herein. Inaccordance with a first embodiment, a slider spring system can beimplemented that includes a plurality of intermediate sliders drivenindependently by a rotating index gear, wherein each intermediate slideramong the plurality of intermediate sliders comprise at least one slot(preferably two slots) for controlling movement when contacted by therotating index gear.

Such a system can also include a single spring for maintaining andretuning the plurality of intermediate sliders to a rest position afterany of the plurality of intermediate sliders are moved by the rotatingindex gear. Each intermediate slider among the plurality of intermediatesliders can comprise: a Point A located at a center of the slot nearestthe rotating index gear; a Point B located at a center of a straightslot nearest a pawl and the plurality of intermediate sliders; and aPoint B located at a center of a contact for the single spring. Point Bmoves primarily along an x-axis to drive the pawl, a lock slider or asuper lock slider, wherein the straight slot accommodates a movement ofPoint B primarily along the X-axis for driving the pawl, the lock slideror the super lock slider.

Point A generates adequate x-axis movement at the Point B whileproviding y-axis movement at Point A to allow the rotating index gear toclear when driving rotation thereof is completed. The single spring,when located at Point C returns an intermediate slider among theplurality of intermediate sliders to the rest position to await asubsequent movement by the rotating index gear. Such a single springcomprises a return spring. Additionally, the slot at the Point A can beconfigured to provide similar movement at the Point B while forcing amovement at the Point C to be radial or to the a natural path of thesingle spring during coiling thereof. Such intermediate sliders and thesingle spring can be adapted for use with a centrifugal clutch.

In accordance with a second embodiment, a spring apparatus can beimplemented, which includes a spring for use in a clutch mechanism,wherein the spring is configured to avoid coil clash and end wirelengths of the spring are positioned in order to center the clutchspring without additional features thereof. Additionally, bend radii anda wire diameter associated with the spring. Such a spring can be adaptedfor use in a centrifugal clutch and/or an automobile latch.

In accordance with a third embodiment, a spring apparatus can beimplemented, which includes a leaf spring for use in a clutch mechanism,wherein the leaf spring is configured to avoid coil clash and end wirelengths of the leaf spring are positioned in order to center the leafspring without additional features thereof. Bend radii and a wirediameter associated with the leaf spring. The leaf spring can be adaptedfor use in a centrifugal clutch and/or automobile latch.

In accordance with a fourth embodiment, a methodology and system forbalancing a centrifugal clutch can be implemented. A 3-dimensional modelof a centrifugal clutch assembly in an engaged position thereof can beestablished and thereafter, a mass center of the centrifugal clutchassembly can be calculated. A distance from the axis of rotation of thecentrifugal clutch assembly can be determined. Thereafter, associatedpart features of the centrifugal clutch assembly can be modified inorder to move the mass center; and repeating as necessary establishing a3-dimensional model of a centrifugal clutch assembly in an engagedposition thereof, calculating a mass center of the centrifugal clutchassembly, determining a particular distance from an axis of rotation ofthe centrifugal clutch assembly, and modifying part features of thecentrifugal clutch assembly in order to move the mass center in order toverify the axis of rotation and thereby balance the centrifugal clutchassembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, in which like reference numerals refer toidentical or functionally-similar elements throughout the separate viewsand which are incorporated in and form a part of the specification,further illustrate the present invention and, together with the detaileddescription of the invention, serve to explain the principles of thepresent invention.

FIG. 1 illustrates a stress plot for a conventional latch spring, whichcan be evaluated in order to determine optimal parameters for the designof an improved latch spring;

FIG. 2 illustrates a stress plot for a conventional latch spring, whichcan be evaluated in order to determine optimal parameters for the designof an improved latch spring;

FIG. 3 illustrates a side view of an intermediate slider springapparatus, in accordance with a first embodiment;

FIG. 4 illustrates a conventional latch spring;

FIG. 5 depicts a stress plot associated with the conventional springdepicted in FIG. 4;

FIG. 6 depicts a stress plot associated with the conventional springdepicted in FIG. 4;

FIG. 7 illustrates an improved latch spring, which can be implemented inaccordance with the second embodiment;

FIG. 8 illustrates a defection plot of a spring, in accordance with thesecond embodiment;

FIG. 9 illustrates a stress plot of a spring in accordance with thesecond embodiment;

FIG. 10 illustrates a leaf spring, which can be adapted for use with acentrifugal clutch, in accordance with a third embodiment;

FIG. 11 illustrates a deflection plot of the leaf spring depicted inFIG. 10, in accordance with the third embodiment;

FIG. 12 illustrates a stress plot of the leaf spring depicted in FIG.10, in accordance with the third embodiment;

FIG. 13 illustrates an alternative leaf spring, which can be adapted foruse with a centrifugal clutch, in accordance with the third embodiment;

FIG. 14 illustrates a deflection plot of the alternative leaf springdepicted in FIG. 13, in accordance with the third embodiment;

FIG. 15 illustrates a stress plot of the alternative leaf springdepicted in FIG. 13, in accordance with the third embodiment;

FIG. 16 illustrates a high-level flow chart of logical operations, whichcan be implemented in order to balance a centrifugal clutch, inaccordance with a fourth embodiment; and

FIG. 17 illustrates a block diagram of data-processing systems, whichcan be implemented in accordance with the fourth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The particular values and configurations discussed in these non-limitingexamples can be varied and are cited merely to illustrate at least oneembodiment of the present invention and are not intended to limit thescope of the invention.

First Embodiment: Intermediate Slider Optimization

FIG. 3 illustrates a side view of an intermediate slider springapparatus 300, which can be implemented in accordance with a firstembodiment. As indicated earlier, some latch designs contain a springwith an axis parallel to the plane of intermediate sliders with two legscontacting each side of a Point C so that movement in either directionconstitutes coiling of the spring. Such a design is inadequate becausethe movement of the spring is not purely in coiling the spring, but alsoalong the axis, which functions to spread or compress the coilstogether. The stress on the two legs is thus too great, leading topremature failure of the latch incorporating such a spring andintermediate sliders.

In accordance with a first embodiment, an intermediate sliderconfiguration for apparatus 300 can be implemented to solve the problemof fatigue failure in the intermediate slider return spring by speciallydesigning a slot 304 at Point A to provide similar movement at Point Bwhile forcing the movement at Point C to be radial to the natural pathof the spring legs during coiling. Removing the axial movement of thespring and replacing it with pure radial movement therefore can allowthe spring apparatus 300 to be applied as intended and extend the lifeof the spring to typical coil spring values. An abutment 302 configuredfrom spring apparatus 300 can be contacted by an index gear. Theintermediate slider rides on pins at points A and B, such that slotsthereof can determine the working motion. Note that spring legs can makecontact at point C.

The spring apparatus 300 can be rotated 90 degrees so that the axis isperpendicular to the plane of the intermediate sliders and the legs canbe bent 90 degrees to contact the sliders at point C. Instead of leavingthe spring movement as an afterthought, the movement at Point C can beused as a driver to the ultimate latch design. The slot 306 at Point Bcan be used to retain the x-axis movement at Point B, but the slot 304at Point A, which originally was implemented as an inverted V pattern,can be redefined by the movement at B and C as drivers. CAD (ComputerAided Design) software, including 3-dimensional design software thereof,can be utilized to dictate the movement at B and C, and plot theresultant movement at Point A. A slot can then be generated from theresultant path and incorporated into the intermediate sliders. Once theoptimized slot at A is defined, the model thereof can be easilyconfirmed by moving the drivers of the motion to Point A and Point Bwhile plotting travel at Point C. The radial path center at Point C thusdefines the axis center of the spring.

Three intermediate sliders can be driven independently by a rotatingindex gear. A single spring can maintain and return all intermediatesliders to a rest position after any of the three are moved by the indexgear. Two slots in the intermediate slider can control the movement ofthis part when contacted by the index gear. It can be appreciated, ofcourse, that reference to “three” intermediate sliders is provided forillustrative purposes only. In accordance with alternative embodiments,additional intermediate sliders may be implemented, depending upondesign considerations.

For illustrative purposes, movement can be described by reference tothree points on the intermediate slider. At the center of the slotnearest the index gear, Point B is the center of the straight slotnearest the pawl and sliders, whereas Point C is the center of contactfor the return spring. Point B should preferably move along the x-axisto drive either a pawl or a super lock slider (i.e., depends on whichintermediate slider is being driven). The straight slot 306 at Point Bcan accommodate this requirement. The slot 304 at Point A is morecomplicated because it must generate adequate x-axis movement at PointB, while also providing y-axis movement at Point A to allow the indexgear to clear when driving rotation is completed. When the index geardrives and then clears the intermediate slider, the spring at Point Creturns the intermediate slider to the rest position to await asubsequent movement by the index gear.

Automotive latching systems may require the use of a clutch springmechanism that includes a return spring, which generally biases thelocation of the abutment to the disengaged position. Some conventionaldesigns can be overstressed, which leads to a short life cycle for theclutch spring mechanism. For example, the clutch and/or clutch springmechanism can fracture during clutch testing.

It is thus desirable to optimize latching system components, such as,for example, spring mechanisms and in particular, clutch springmechanisms and devices. The principal requirements for a successfulspring design including tightening manufacturing tolerances, determiningwhich forces the design actually requires (e.g., low and upper limits),and determining the maximum allowable footprint for the channel in orderto provide the maximum design space available for further optimizationand for meeting such requirements.

An embodiment can thus be implemented to optimize a clutch springmechanism design by determining the optimum number of coils and shapewhile utilizing standard bend radii and wire diameter. The end of wirebends, for example, can be eliminated to avoid coil clash, while the endwire length can be modified to center the spring without added features.The overall size and the pocket containing the spring can thus beincreased. The bend radius can be increased to an acceptablemanufacturing size.

In general, sidewalls of the channel containing the spring can beimplemented, and two-dimensional surface-to-surface contact elements canbe added to create real-world boundaries. With such contact elements inplace, spring flexure can be restricted if any of the loops thereof bumpinto each of the channel wall. A suggested coefficient of friction formodeling such a device can be, for example, a coefficient of friction of0.3. It can be appreciated of course, that such a value is merelypresented for illustrative purposes only and is not considered alimiting feature of the embodiments disclosed herein.

Contact elements can also be strung between each loop of the spring.Unlike conventional spring mechanisms, however, this type of contactelement can be configured to take into consideration the thickness ofthe wire, while not allowing for the center line of each loop to movecloser than the wire diameter.

Coil self-contact and contact with the walls can also be monitored. Aself-contact (i.e., contact of one loop to the other) is acceptable, butcontact between the loops and side walls is not acceptable. The chiefreason for such choices is that if there is any relative motion duringcontact (e.g., friction with the walls), such relative motion duringcontact may wear away the wire and lead to failure. In conventionalsystems, this is especially a problem at the outside edges of the loop,which is the most likely spot to contact the channel side thereof,because stresses are highest at this point and any loss in wirethickness can result in serious damage to the actual coil and springmechanism system. Conversely, when the loops touch each other, as inself-contact, there will likely be very little relative motion and sovery little wearing should occur that such a situation is likely abenign contact. Such features represent significant improvements toreplicate improved latching spring mechanisms.

FIG. 4 illustrates a conventional latch spring 400, which is subject toseveral problems, including the inability to meet the aforementionedprincipal requirements for a successful spring design includingtightening manufacturing tolerances, determining which forces the designactually requires (e.g., low and upper limits), and determining themaximum allowable footprint for the channel in order to provide themaximum design space available for further optimization and for meetingsuch requirements. Spring 400 suffers from a short fatigue life, becausespring 400 tends to contact itself when compressed, thereby resulting inearly fatigue failure. Such a condition is known as “coil clash”. Thus,any successful design for a latch spring should not allow “self-contact”anywhere in the spring.

Note that in the illustration of FIG. 4, the cross-section of spring 400is actually circular, rather than square as shown therein. Thedimensions of spring 400 generally include a diameter of 0.2 mm, aformed width of 3.9 mm with 0.4 outer corner radii, an overall length ofapproximately 10 mm and a total of 4.5 loops. For wire drawn to thissmall of a diameter, the tensile and yield stresses are approximatelythe same (e.g., 325 ksi). This is a very high strength material andthere is apparently very little room for additional strain before thematerial breaks. A sample of spring 400 can be tested by bending oneloop of spring 400 up, so that it will be found to break after onlyapproximately 45 degrees deflection, verifying this extreme condition.

FIG. 5 depicts a stress plot 500 associated with the conventional spring400 depicted in FIG. 4. Thus, data associated with conventional spring400 is generally shown in stress plot 500 of FIG. 5. In stress plot 500,the side rails 502, 504 represent the edge of the channel 506 that thespring is intended to be trapped within. Note that the displacement andstress plots are shown as line plots.

FIG. 6 depicts a stress plot 600 associated with the conventional spring400 depicted in FIG. 4. Note that in FIG. 6, colors are generallysuperimposed on the lines for stress plots to indicate stress valueversus location. Also note that the model of stress plot 500 inassociation with conventional spring 400 accounts for the actualthickness of the spring 400, even though such a thickness is notactually shown in such a plot.

Stress plot 500 generally indicates the spring compression forces forthe conventional spring 400 were found to be as follows:

-   2.5 mm compression: 0.15956 lbs., and coil clash does occur at this    level of compression.-   5.0 mm compression: 0.33769 lbs., and coil clash remains at this    level of compression.

With so much coil clash occurring, spring 400 is effectively always inself-contact, regardless of whether spring 400 is in a low or highcompressed state. Thus, spring 400 represents a poor spring design.Spring 400 is therefore likely to be compressed in unexpected manners,due to self-contact, during the switching cycle. In addition, as thespring contacts itself, gouges, or is subject to wear, design life isfurther reduced.

The basic problem with spring 400, as evidence by stress plots 500 and600, is the difficulty involved in maintaining current forces atcompressions of 2.5 and 5.0 mm, while lowering stresses to prolong life.To solve this problem, three approaches can be taken. An improved springdesign should preferably use round wire only, possess a rectangularcross-section (e.g., a leaf spring), and repeat the latter, whileremoving the curled end of the spring that tends to touch itself whenthe spring is compressed.

Additionally, an improved spring design that overcomes the problems ofspring 400 can be implemented in the context of an expanded designspace, thereby allowing for larger springs. The maximum formed springwidth can be increased from a conventional value of, for example 3.9 mmto 10 mm (0.400″), while the maximum spring height (e.g., for the caseof a leaf spring) can be increased from a conventional value of, forexample, 0.2 mm up to 3.2 mm (0.125″). In an improved spring design, thenumber of loops can also be allowed to vary from a conventional valueof, for example, 4.5 to whatever an amount is required. Finally, theouter corner radius of the improved spring can be allowed to vary from aconventional value of, for example, 0.4 mm, to whatever value functionsthe best, with one exception.

Because bare wire stock is formed into the spring (likely at elevatedtemperatures to be able to withstand the amount of strain that isrequired), it has been determined that the corner radius/thickness ratioshould preferably not become too small or the wire will likely breakduring formation thereof. Thus, to provide a realistic limitation, theamount of strain at the corner bend should likely not exceed a value of33%. Such a value can be calculated simply by dividing the outer radiusminus the center-line radius of the spring by the same center-lineradius.

Some general trends and observations can be set forth at this point.Decreasing the number of loops can prevent coil clash, but doing so mayalso increase compression forces and stresses. Additionally, increasingthe wire diameter can increase stress and compression forces greatly.Increasing the spring width tends to decrease stress and compressionforce. Finally, increasing the corner bend radius tends to decreasestress and force.

FIG. 7 illustrates an improved latch spring 700, which can beimplemented in accordance with the second embodiment. Spring 700 can beimplemented in the context of round wire configurations. Spring 700 mayinclude a wire diameter of approximately 0.31 mm, along with the numberof loops at 1.5, an outside corner bend radius of approximately 0.70 mm,and a formed spring width of approximately 9.9 mm. The design of spring700 can possess a maximum stress of 378 ksi. It is important to notethat such parameters are merely illustrative values only and arepresented in the context of one possible example. Thus, other parameterscan be implemented in accordance with alternative versions of the secondembodiment.

FIG. 8 illustrates a defection plot of spring 700, in accordance withthe second embodiment. FIG. 9 illustrates a stress plot of spring 700 inaccordance with the second embodiment. Note that the cross-section isactually circular, even though it appears as a square, due to CADsoftware graphic output. Based on FIGS. 8-9, it can thus be appreciatedthat although the number of cycles to failure is unknown, an overallimprovement to both performance and stress resistance is evident. Spring700 therefore contains an optimum number of coils and shape whileutilizing standard bend radii and wire diameter. The end of wire bendscan be eliminated in spring 700 in order to avoid coil clash.Additionally, the end wire length of spring 700 is modified to centerspring 700 without additional support features. The overall size and thepocket containing spring 700 can be increased. The bend radius can alsobe increased to a manufacturing acceptable size.

Third Embodiment: Leaf Spring Design for Centrifugal Clutch

FIG. 10 illustrates a leaf spring 1000, which can be adapted for usewith a centrifugal clutch, in accordance with a third embodiment. Leafspring 1000 represents an optimal design with a rectangularcross-section and a shape that is somewhat reminiscent of “linguine”pasta. In the example of FIG. 10, leaf spring 1000 can possess a wirecross-sectional with of approximately 0.13 mm, a wire cross-sectionalheight of approximately 3.0 mm, a number of loops of 1.5, an outsidecorner bend radius of 1.0 mm, and a formed spring width of 10 mm. Thedesign of leaf spring 1000 can possess a maximum stress of, forexample,138 ksi. It can be appreciated, of course, that such parametersare merely suggested values and are not considered limited features ofthe third embodiment. Such parameters are presented merely forillustrative and exemplary purposes only. FIG. 10 generally representsan element plot of leaf spring 1000. FIG. 11 illustrates a deflectionplot 1100 of leaf spring 1000, while FIG. 12 represents a stress plot1200 of leaf spring 900.

FIG. 13 illustrates an alternative leaf spring 1300, which can beadapted for use with a centrifugal clutch, in accordance with the thirdembodiment. FIG. 14 illustrates a deflection plot 1400 of thealternative leaf spring 1300 depicted in FIG. 13, in accordance with thethird embodiment. FIG. 15 illustrates a stress plot 1500 of thealternative leaf spring 1300 depicted in FIG. 13, in accordance with thethird embodiment. Leaf spring 1300 represents another optimal design fora spring mechanism for use a clutch, such as a centrifugal clutch. Leafspring 1300 can be implemented as a small leaf spring (i.e., rectangularcross-section with a shape somewhat like “linguine” pasta). Leaf spring1300 is similar to leaf spring 1000, but is implemented without thelittle curled ends of the spring, which are removed so that they do notexacerbate “coil clash”.

In general, leaf spring 1300 can possess a wire-cross sectional width ofapproximately 0.14 mm, a wire cross-sectional height of approximately3.1 m, a number of loops of 2.0, an outside corner bend radius ofapproximately 0.8 mm formed spring width of approximately 10 mm. Such adesign can possess a maximum stress of approximately 110 ksi. It can beappreciated, of course, that such parameters are merely suggested valuesand are not considered limited features of the third embodiment. Suchparameters are presented merely for illustrative and exemplary purposesonly.

The aforementioned leaf spring embodiments thus represent an evengreater improvement over round wire. Such a design is preferred becauseanother half of loop spring can potentially be added with causing coilclash. By implementing such leaf spring embodiments, stresses can bedecreased by approximately 80% over conventional spring mechanisms andcan operate at safe levels so that the spring can possess infinite life.

Fourth Embodiment: Centrifugal Clutch CAD Balanced Design

Conventional centrifugal clutches typically suffer from imbalance duringoperation, particularly in the context of motor and clutch assemblies.Such assemblies typically remain unbalanced during performanceconditions. For example, upon testing a conventional clutch on a motorfor 26,000, it has been observed that motor bearings wear significantlyand therefore are predicted not to withstand the required cycles. Suchan assembly must be accurately balanced in order to improve vibrationand bearing life in the motor. Despite efforts to implement balancing ina centrifugal clutch such as, for example, utilizing software analysistools to properly balance the centrifugal clutch assembly, it has beendetermined that such designs when subject to testing can wear away thecontacts in the motor.

In accordance with a fourth embodiment, an analysis tool can be utilizedto assemble a 3-dimensional model of the clutch into its engagedposition. A 3-dimensional model of the clutch can be assembled utilizingan analysis tool, such as 3-dimensional CAD software. The mass center ofthe clutch assembly can then be calculated. Thereafter, the distancefrom the axis of rotation can be determined and the part featuresthereof modified in order to move the mass center. The model analysiscan then be rerun. The prior steps can then be rerun until the productmass center is on the axis of rotation. Additional components forrotating the clutch, such as a pinion gear GA, can also be consideredutilizing this procedure in order to ensure overall proper balancing.

FIG. 16 illustrates a high-level flow chart 1600 of logical operations,which can be implemented in order to balance a centrifugal clutch, inaccordance with a fourth embodiment. As indicated at block 1602, theprocess can be initiated. Thereafter, as depicted at block 1604, a3-dimensional model of the clutch into its engaged position. Next, asindicated at block 1606, the mass center of the clutch assembly can becalculated. Thereafter, as described at block 1608, the distance fromthe axis of rotation can be determined, followed by processing of theoperation depicted at block 1610, in which the part features thereof aremodified in order to move the mass center. The model analysis can thenbe rerun as indicated at block 1612 (i.e., repeat analysis . . . yes orno?). The prior steps can then be rerun until the product mass center isverified on the axis of rotation, as depicted at block 1615. Additionalcomponents for rotating the clutch, such as a pinion gear GA, can alsobe considered utilizing this procedure in order to ensure overall properbalancing. The process can then terminate, as indicated at block 1616.

It can be appreciated that the operational steps depicted in FIG. 16generally represent operations that may be utilized in accordance with avariety of embodiments. Such operational steps can be utilized toimplement methods, systems and program products thereof. Suchoperational steps may also be implemented in the form of softwaremodules. Such modules are generally collections of routines and datastructures that perform particular tasks or implement particularabstract data types and/or instructions for processing via a processorand/or other data-processing device. Modules are typically composed oftwo portions: an interface, which lists constants, data types,variables, routines, subroutines, and so forth, which may be accessed byother modules, routines, or subroutines; and an implementation, which isaccessible only to the module and which contains source code thatactually implements the routines in the module.

Thus, for example, the operation depicted at block 1604 can beimplemented as a module for assembling a 3-dimensional model of theclutch into its engaged position. Similarly, the operation depicted atblock 1606, can be implemented as a module for calculating the masscenter of the clutch assembly. The operation described at block 1608 canbe implemented as module for determining the distance from the axis ofrotation. The operation illustrated at block 1610 can be implemented asa module for modifying part features of the clutch assembly order tomove the mass center. The operation described at block 1612 can beimplemented as a module which determines whether or not to repeat theoperations indicated at blocks 1604 to 1610. Similarly, the operationindicated at block 1614 can be implemented as a module for verifyingthat the product mass center is verified on the axis of rotation, asdepicted at block 1615. Such modules can be stored in a memory unit of adata-processing system and processed via one or more microprocessorsassociated with such a system.

FIG. 17 illustrates a data-processing system 1700, which can beimplemented in accordance with the fourth embodiment. In general, system1700 can include a CPU (Central Processing Unit) 1720, such as aconventional microprocessor, and a number of other units interconnectedvia system bus 1703. System 1700 includes random access memory (“RAM”)1722, read only memory (“ROM”) 1728, display adapter 1736, which canconnect to a display device 1738, and I/O adapter 1724 for connectingperipheral devices (e.g., disk and tape drives 1726) to system bus 1703.Data-processing system 1700 can further include a user interface adapter1730 for connecting devices such as a keyboard, mouse, speaker,microphone, and/or other user interface devices, such as a touch screendevice (not shown), to system bus 1703. Communication adapter 1734 canconnect data-processing system 1700 to a data-processing and or computernetwork 1732 such as, for example, the Internet or World Wide Web.

Data-processing system 1700 also includes a plurality of modules thatreside within a memory 1701 in the context of machine-readable media todirect the operation of data-processing system 1700. Any suitablemachine-readable media may retain such modules, such as memory 1700, RAM1722, ROM 1728, a magnetic diskette, magnetic tape, or optical disk (thelast three being located in disk and tape drives 1726). Any suitableoperating system and associated graphical user interface (e.g.,Microsoft Windows) can direct microprocessor 1720.

A module 1704 for assembling a 3-dimensional model of the clutch intoits engaged position can be maintained by memory 1701. Similarly, a masscalculation module 1706 for calculating the mass center of the clutchassembly can be stored within memory 1701. Also, a distancedetermination module 1708 for determining the distance from the axis ofrotation can be stored within memory 1701. A modification module 1710for modifying part features of the clutch assembly order to move themass center can be also be stored within memory 1701. Finally, othermodules for performing other operations can also be stored within memory1701, including modules which function as the operation system fordata-processing system 1701.

The embodiments and examples set forth herein are presented to bestexplain the present invention and its practical application and tothereby enable those skilled in the art to make and utilize theinvention. Those skilled in the art, however, will recognize that theforegoing description and examples have been presented for the purposeof illustration and example only. Other variations and modifications ofthe present invention will be apparent to those of skill in the art, andit is the intent of the appended claims that such variations andmodifications be covered.

The description as set forth is not intended to be exhaustive or tolimit the scope of the invention. Many modifications and variations arepossible in light of the above teaching without departing from the scopeof the following claims. It is contemplated that the use of the presentinvention can involve components having different characteristics. It isintended that the scope of the present invention be defined by theclaims appended hereto, giving full cognizance to equivalents in allrespects.

1. A leaf spring apparatus, comprising: a leaf spring for use inspreading a clutch mechanism, wherein said leaf spring is configured toavoid coil clash and end wire lengths of said leaf spring are positionedin order to center said leaf spring without additional features thereof.2. The apparatus of claim 1 further comprising bend radii and a wirediameter associated with said leaf spring.
 3. The apparatus of claim 1wherein said leaf spring comprises a maximum stress of approximately 110ksi.
 4. The apparatus of claim 1 wherein said leaf spring comprises aplurality of bends.
 5. The apparatus of claim 4 wherein said leaf springcomprises a pasta shaped configuration.
 6. The apparatus of claim 1wherein said leaf spring comprises a plurality of loops.
 7. Theapparatus of claim 1 wherein said leaf spring is configured from a wireand comprises a wire cross sectional width thereof that is rectangularin shape.
 8. The apparatus of claim 1 wherein said leaf spring isadapted for use in a centrifugal clutch.
 9. The apparatus of claim 8wherein said leaf spring is adapted for use with an automobile latch.10. A leaf spring apparatus, comprising: a leaf spring for use in aclutch mechanism, wherein said leaf spring is configured to avoid coilclash and end wire lengths of said leaf spring are positioned in orderto center said leaf spring without additional features thereof; andwherein said leaf spring comprises a pasta-shaped configuration and aplurality of loops thereof such that said leaf spring includes bendradii and a wire diameter associated with said leaf spring.
 11. Theapparatus of claim 10 wherein said leaf spring is configured from a wireand comprises a wire cross sectional width thereof that is rectangularin shape.
 12. The apparatus of claim 11 wherein said leaf spring isadapted for use in a centrifugal clutch.
 13. The apparatus of claim 12wherein said leaf spring is adapted for use with an automobile latch.14. A leaf spring method, comprising the steps of: providing a leafspring for use in a clutch mechanism; configuring said leaf spring toavoid coil clash; and positioning at least one end wire length of saidleaf spring in order to center said leaf spring without additionalfeatures thereof.
 15. The method of claim 14 further comprising the stepof configuring said leaf spring to comprise bend radii and a wirediameter associated only with said leaf spring.
 16. The method of claim14 wherein said leaf spring comprises a maximum stress of approximately110 ksi.
 17. The method of claim 14 further comprising the step ofconfiguring said leaf spring to comprise a plurality of bends.
 18. Themethod of claim 14 further comprising the step of configuring said leafspring to comprise a pasta shaped configuration.
 19. The method of claim18 further comprising the step of configuring said leaf spring tocomprise a plurality of loops thereof.
 20. The method of 14 furthercomprising the step of configuring leaf spring from a wire, wherein saidleaf spring comprises a wire cross sectional width thereof that isrectangular in shape.